Expansion device

ABSTRACT

To provide an expansion device which shortens cool down time when an automotive air conditioner is started under a high-load condition. An expansion device having a differential pressure control valve is configured such that a temperature-sensing actuator (shape-memory alloy spring) is disposed at an refrigerant outlet of the expansion device, and when an air conditioner is started under a high-load condition in which the temperature of refrigerant at the refrigerant outlet is high, the shape-memory alloy spring senses the high temperature, to urge a spring determining a valve-opening point of the differential pressure control valve, whereby the differential pressure control valve is opened in advance or placed in a state capable of opening in response to a very low differential pressure, thereby making it possible to cause refrigerant to flow at a large flow rate until the temperature of refrigerant at the refrigerant outlet is lowered to a temperature assumed when the air conditioner functions.

CROSS-REFERENCE TO RELATED APPLICATIONS, IF ANY

This application claims priorities of Japanese Application No. 2006-229559 filed on Aug. 25, 2006, entitled “EXPANSION DEVICE”.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates to an expansion device, and more particularly to an expansion device for expanding refrigerant in a refrigeration cycle for an automotive air conditioner.

(2) Description of the Related Art

A refrigeration cycle for an automotive air-conditioner is known which comprises a compressor that compresses refrigerant, a condenser or a gas cooler that condenses or cools the compressed refrigerant, a receiver that stores the condensed or cooled refrigerant to separate the same into a gas and a liquid, an expansion device that expands the liquid refrigerant obtained by the gas/liquid separation, and an evaporator that evaporates the expanded refrigerant by heat exchange between the refrigerant and air in a vehicle compartment to return the evaporated refrigerant to the compressor. As the expansion device, a thermostatic expansion device is generally used which senses the temperature and pressure of refrigerant at an outlet of the evaporator, and thereby controls the flow rate of refrigerant sent to the evaporator.

On the other hand, a refrigeration cycle is known which comprises a compressor, a condenser or a gas coolers an evaporator that expands condensed or cooled refrigerant, and an accumulator that stores evaporated refrigerant to separate the same into a gas and a liquid, and returns gaseous refrigerant obtained by the gas/liquid separation to the compressor. One of various types of expansion devices for use in the refrigeration cycle configured as above is a differential pressure control valve that senses differential pressure between pressure at an inlet thereof and pressure at an outlet thereof, and progressively opens as the differential pressure becomes larger (see e.g. Japanese Unexamined Patent Publication No. 2005-249380).

The expansion device disclosed in Japanese Unexamined Patent Publication No. 2005-249380 includes a valve element disposed in a passage through which refrigerant flows, for opening and closing the passage, and a spring for urging the valve element in a valve-closing direction. The expansion device operates such that after the start of the automotive air conditioner, when the pressure at the inlet is increased by the discharge pressure of the compressor and the pressure at the outlet is decreased by the suction pressure of the compressor, to cause the differential pressure to exceed a valve-opening differential pressure set by the spring, the expansion device opens and the valve lift thereof becomes larger as the differential pressure becomes larger.

In the refrigeration cycle using the differential pressure control valve as the expansion device, no differential pressure is generated between the pressure at the inlet of the differential pressure control valve and the pressure at the outlet thereof when the automotive air conditioner is at rest, and hence the differential pressure control valve is in a closed state with the valve element being urged by the spring in the valve-closing direction. When the automotive air conditioner is started, and the compressor starts to operate at maximum displacement, the pressure at the inlet of the expansion device immediately increases. On the other hand, refrigerant on the outlet side of the expansion device is drawn by the compressor, whereby the pressure thereat is about to be lowered. However, the accumulator provided between the expansion device and the compressor inhibits immediate reduction of the pressure, so that the pressure on the inlet side of the expansion device further increases, and when the differential pressure thereacross reaches the valve-opening differential pressure, the expansion device opens. However, if the pressure on the outlet side of the expansion device is difficult to be lowered to hinder generation of a sufficiently large differential pressure, causing a throttled state of refrigerant to be continued, the pressure on the inlet side of the expansion device even further increases. In such a case, the compressor performs displacement control to reduce displacement thereof, thereby preventing the discharge pressure from becoming too high. Reduction of displacement of the compressor at the start of the automotive air conditioner means that the automotive air conditioner is not cooled or it takes a long time before the air conditioner is cooled.

This tendency is conspicuous particularly in a case where carbon dioxide having a very high operating pressure is used as refrigerant in the refrigeration cycle and the automotive air conditioner is started in a state in which the temperature of an engine room is very high. In such a case, before the start of the automotive air conditioner, pressure of refrigerant at the inlet and the outlet of the expansion device has already been made high by radiant heat from the atmosphere at high temperature, the sun, and so forth, and hence load on the automotive air conditioner is very high. When the automotive air conditioner is started in this high-load state, the pressure of refrigerant at the inlet of the expansion device immediately increases from the pressure already made high before the start of the automotive air conditioner to a high-pressure region that is regarded dangerous for the refrigeration cycle. To avoid such an abnormally high pressure, the compressor starts the displacement control toward reduced displacement, so that the automotive air conditioner is difficult to be cooled and it takes a very long time to cool down.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above points, and an object thereof is to provide an expansion device which shortens cool down time when an automotive air conditioner is started under a high-load condition.

To solve the above problem, the present invention provides an expansion device for expanding refrigerant circulating through a refrigeration cycle, comprising a differential pressure control valve that is responsive to differential pressure between pressure at a refrigerant inlet and pressure at a refrigerant outlet, to open, and an actuator that sets valve-opening differential pressure at which the differential pressure control valve opens, to a lower value, when refrigerant at the refrigerant outlet is higher in temperature than a temperature at which the refrigeration cycle is operating in a steady state or higher in pressure than pressure corresponding to the temperature.

Further, the present invention provides an expansion device for expanding refrigerant circulating through a refrigeration cycle, comprising a first differential pressure control valve that is responsive to differential pressure between pressure at a refrigerant inlet and pressure at a refrigerant outlet, to open, a second differential pressure control valve that has a valve hole formed between the refrigerant inlet and the refrigerant outlet, and has a diameter larger than that of the first differential pressure control valve, and an actuator that sets valve-opening differential pressure at which the second differential pressure control valve opens, to a lower value, when refrigerant at the refrigerant outlet is higher in temperature than a temperature at which the refrigeration cycle is operating in a steady state or higher in pressure than pressure corresponding to the temperature.

The above and other objects, features and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings which illustrate preferred embodiments of the present invention by way of example.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a system diagram showing a refrigeration cycle to which is applied the expansion device according to the present invention.

FIG. 2 is a central longitudinal cross-sectional view of the arrangement of an expansion device according to a first embodiment.

FIG. 3 is a diagram showing a temperature-spring load characteristic of a temperature-sensing actuator.

FIG. 4 is a diagram showing changes in the restriction passage cross-sectional area of the expansion device, with respect to changes in the differential pressure of the expansion device.

FIG. 5 is a central longitudinal cross-sectional view of the arrangement of an expansion device according to a second embodiment.

FIG. 6 is a central longitudinal cross-sectional view of the arrangement of an expansion device according to a third embodiment.

FIG. 7 is a central longitudinal cross-sectional view of the arrangement of an expansion device according to a fourth embodiment.

FIG. 8 is a central longitudinal cross-sectional view of the arrangement of an expansion device according to a fifth embodiment.

FIG. 9 is a central longitudinal cross-sectional view of the arrangement of an expansion device according to a sixth embodiment.

FIG. 10 is a central longitudinal cross-sectional view of the arrangement of an expansion device according to a seventh embodiment.

FIG. 11 is a central longitudinal cross-sectional view of the arrangement of an expansion device according to an eighth embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereafter, embodiments of the present invention will be described in detail with reference to the drawings showing expansion devices applied to a refrigeration cycle for an automotive air conditioner, using carbon dioxide as refrigerant, by way of example.

FIG. 1 is a system diagram showing a refrigeration cycle to which is applied the expansion device according to the present invention. FIG. 2 is a central longitudinal cross-sectional view of the arrangement of an expansion device according to a first embodiment. FIG. 3 is a diagram showing a temperature-spring load characteristic of a temperature-sensing actuator. FIG. 4 is a diagram showing changes in the restriction passage cross-sectional area of the expansion device, with respect to changes in the differential pressure of the expansion device.

As shown in FIG. 1, the refrigeration cycle comprises a compressor 1 for compressing refrigerant, a gas cooler 2 for cooling the compressed refrigerant, an expansion device 3 for throttling and expanding the cooled refrigerant, an evaporator 4 for evaporating the expanded refrigerant, an accumulator 5 for storing surplus refrigerant in the refrigeration cycle and separating refrigerant in a gaseous phase from the evaporated refrigerant to send the gaseous refrigerant to the compressor 1, and an internal heat exchanger 6 for performing heat exchange between refrigerant flowing from the gas cooler 2 to the expansion device 3 and refrigerant flowing from the accumulator 5 to the compressor 1. In FIG. 1, arrows indicate respective flows of refrigerant.

The refrigeration cycle operates such that refrigerant in a gaseous phase is compressed into high-temperature, high-pressure refrigerant by the compressor 1; the high-temperature, high-pressure refrigerant is cooled by the gas cooler 2; the cooled refrigerant is throttled and expanded to be changed into low-temperature, low-pressure refrigerant by the expansion device 3; and the low-temperature, low-pressure refrigerant is evaporated by the evaporator 4. In the process in which refrigerant is expanded by the expansion device 3, the refrigerant is changed into a two-phase gas-liquid state, and when the refrigerant in the two-phase gas-liquid state is evaporated by heat exchange in the evaporator 4 between the refrigerant and air in the vehicle compartment, the refrigerant cools the air in the vehicle compartment by depriving the air of latent heat of vaporization.

Further, in the refrigeration cycle using carbon dioxide as refrigerant, it is a common practice to dispose the internal heat exchanger 6 that performs heat exchange between refrigerant at the outlet of the gas cooler 2 and refrigerant at the inlet of the compressor 1, so as to lower the enthalpy of refrigerant at the inlet of the evaporator 4 to thereby enhance the cooling power of the refrigeration cycle.

The internal heat exchanger 6 is formed therein with a high-pressure passage for allowing high-pressure refrigerant introduced from the gas cooler 2 to flow therethrough, and a low-pressure passage for allowing low-pressure refrigerant introduced from the accumulator 5 to flow therethrough, and the expansion device 3 is disposed at the outlet of the high-pressure passage.

As shown in FIG. 2, the expansion device 3 disposed in the internal heat exchanger 6 has a body 11. The body 11 has an upper end formed with a refrigerant inlet 12 for introducing refrigerant from the high-pressure passage of the internal heat exchanger 6, and the refrigerant inlet 12 is provided with a strainer 13 for blocking foreign matter in refrigerant from entering the expansion device 3. Further, the body 11 has a refrigerant outlet 14 formed in a side portion thereof, and a valve hole 15 formed to extend along the axis thereof between the refrigerant inlet 12 and the refrigerant outlet 14. A valve element 16 is axially movably disposed in a space communicating with the refrigerant outlet 14, for opening and closing the valve hole 15. The valve element 16 is integrally formed with a piston 17 which is disposed in a hollow cylindrical portion integrally formed with a lower portion of the body 11, as viewed in FIG. 2, in a manner movable along the axis of the hollow cylindrical portion. On a side of the piston 17 opposite to a side thereof where the valve element 16 is disposed, a spring 18 is disposed for urging the valve element 16 in the valve-closing direction. Since the valve element 16 is urged by the spring 18 in the direction of closing the valve hole 15, the valve element 16 and the spring 18 constitute a differential pressure control valve which is responsive to differential pressure between pressure at the refrigerant inlet 12 and pressure at the refrigerant outlet 14, to open.

The spring 18 is received by an adjustment screw 19 screwed into the hollow cylindrical portion of the body 11, and by adjusting the axial screwing amount of the adjustment screw 19 into the body 11, it is possible to set valve-opening differential pressure at which the differential pressure control valve opens. The valve element 16 is provided with an orifice 20 for bypassing the differential pressure control valve. The orifice 20 is provided for allowing refrigerant to flow at a minimum flow rate which is required for causing compressor-lubricating oil circulating together with the refrigerant through the refrigeration cycle to flow when the differential pressure control valve is closed. Disposed in the space communicating with the refrigerant outlet 14 is a shape-memory alloy spring 21 for urging the valve element 16 in the valve-opening direction. The shape-memory alloy spring 21 forms a temperature-sensing actuator which senses the temperature of refrigerant at the refrigerant outlet 14 of the expansion device 3, and acts to actuate the differential pressure control valve in the valve-opening direction when the sensed refrigerant temperature exceeds a predetermined value. The shape-memory alloy spring 21 disposed in the refrigerant outlet 14 of the expansion device 3 has a bidirectional shape memory effect that a spring load thereof reversibly changes with respect to temperature cycling, and as shown in FIG. 3, has characteristics that its spring load is small and the rate of change in spring load with respect to a change in temperature is also very small at temperatures lower than the transformation temperature (150 in the illustrated example), whereas at temperatures higher than the transformation temperature, the rate of increase in spring load with respect to a rise in temperature suddenly increases, and further at temperatures not lower than a predetermined temperature (25° in the illustrated example) which is even higher than the temperatures higher than the transformation temperature, the spring load is saturated to stop increasing.

In the expansion device 3 configured as above, when the automotive air conditioner is started, and is being operated in a steady state, the outlet temperature of the expansion device 3 is normally not higher than 15°, and therefore the differential pressure control valve has a characteristic indicated by a thick solid line in FIG. 4. More specifically, when the outlet temperature of the expansion device 3 is not higher than 15°, the shape-memory alloy spring 21 has the minimum spring load, so that when the differential pressure ΔP between the pressure at the refrigerant inlet 12 of the expansion device 3 and the pressure at the refrigerant outlet 14 of the same is sufficiently small, the spring 18 overcomes the spring load of the shape-memory alloy spring 21, to urge the valve element 16 in the valve-closing direction, whereby the differential pressure control valve is closed. At this time, the differential pressure control valve forms a restriction passage which has a restriction passage cross-sectional area determined by the orifice 20.

When the differential pressure ΔP between the pressure at the refrigerant inlet 12 of the expansion device 3 and the pressure at the refrigerant outlet 14 of the same rises to exceed ΔP1, the differential pressure control valve opens, whereafter the valve element 16 lifts in proportion to a rise in the differential pressure to increase the restriction passage cross-sectional area whereby the flow rate of refrigerant increases.

On the other hand, when the automotive air conditioner is at rest, and the outside air temperature is as high as 40°, for example, refrigerant has a very high temperature at every location in the refrigeration cycle due to the ambient temperature. Of course, the outlet temperature of the expansion device 3 has also become high, and the shape-memory alloy spring 21 senses the outlet temperature to have the maximum spring load. At this time, if the spring load of the shape-memory alloy spring 21 is set to be approximately equal to the spring load of the spring 18, the valve-opening differential pressure at which the differential pressure control valve opens is set to be approximately equal to zero, and hence when the automotive air conditioner is started in this state, and once refrigerant flows even at a slight flow rate, the differential pressure control valve instantly fully opens, whereby the restriction passage cross-sectional area becomes maximum, as shown in FIG. 4 as a case of the outlet temperature being not lower than 25°.

It should be noted that when the outlet temperature of the expansion device 3 is very high, if the spring load of the shape-memory alloy spring 21 is set to be larger than the spring load of the spring 18, the shape-memory alloy spring 21 overcomes the spring load of the spring 18, to urge the valve element 16 in the valve-opening direction. This makes it possible to place the differential pressure control valve in an open state before the start of the automotive air conditioner.

As described above, in a state in which the ambient temperature is so high that load on the automotive air conditioner is very high, the shape-memory alloy spring 21 senses the outlet temperature of the expansion device 3, to thereby set the valve-opening differential pressure at which the differential pressure control valve opens to a lower value, or hold the differential pressure control valve in the open state. Therefore, it is possible to causes refrigerant to flow at a large flow rate when the automotive air conditioner is started. For the expansion device 3 to be open at the start of the automotive air conditioner, or immediately after the start thereof means that pressure on the inlet side of the expansion device 3 is prevented from becoming abnormally high immediately after the start of the compressor 1. Further, for refrigerant to flow at a large flow rate immediately after the start of the compressor 1 means that the compressor 1 can continue operation at maximum displacement. Therefore, it is possible to lower the outlet temperature of the expansion device 3 soon, whereby cool down time can be shortened.

As the compressor 1 continues operation at maximum displacement, the outlet temperature of the expansion device 3 becomes lower before long. When the outlet temperature of the expansion device 3 becomes lower than the predetermined temperature (25° in the illustrated example), the spring load of the shape-memory alloy spring 21 progressively decreases. As a result, the valve element 16 is pushed by the spring 18 to move in the valve-closing direction, and accordingly the restriction passage cross-sectional area is also progressively reduced. At this time, the valve-opening differential pressure at which the differential pressure control valve opens also increases from the state approximately equal to zero, and when the outlet temperature of the expansion device 3 lowers to 20°, the valve-opening differential pressure at which the differential pressure control valve opens shifts to ΔP0, and when the outlet temperature of the expansion device 3 further lowers to 15°, the valve-opening differential pressure shifts to ΔP1.

FIG. 5 is a central longitudinal cross-sectional view of the arrangement of an expansion device according to a second embodiment. In FIG. 5, component elements identical to those shown in FIG. 2 are designated by identical reference numerals, and detailed description thereof is omitted.

The expansion device 31 according to the second embodiment is configured such that the differential pressure control valve (hereinafter referred to as “the first differential pressure control valve”) of the expansion device 3 according to the first embodiment, and a second differential pressure control valve having a larger port diameter than that of the first differential pressure control valve function in parallel with each other, whereby when the outlet temperature of the expansion device 3 is high, the shape-memory alloy spring 21 opens the second differential pressure control valve, thereby allowing refrigerant to flow at an even larger flow rate.

More specifically, in the expansion device 31, the second differential pressure control valve is formed in the body 11 between the refrigerant inlet 12 and the refrigerant outlet 14, and has a valve hole 32 having a larger inner diameter than that of the valve hole of the first differential pressure control valve, with a valve element 33 axially movably disposed in the space communicating with the refrigerant outlet 14, for opening and closing the valve hole 32. The valve element 33 is integrally formed with a piston 34 axially movably disposed in a hollow cylindrical portion which is integrally formed with a lower portion of the body 11, as viewed in FIG. 5. On a side of the piston 34 where the valve element 33 is provided, the shape-memory alloy spring 21 is disposed for urging the valve element 33 in the valve-opening direction, and on a side of the piston 34 opposite to a side thereof where the valve element 33 is provided, a spring 35 is disposed for urging the valve element 33 in the valve-closing direction. An adjustment screw 36 is screwed into an open end of the hollow cylindrical portion of the body 11, such that the spring loads of the shape-memory alloy spring 21 and the spring 35 can be adjusted.

The first differential pressure control valve uses a hole axially formed through the valve element 33 of the second differential pressure control valve as the valve hole 15. The valve element 16 and the piston 17 are axially movably accommodated in the piston 34 of the second differential pressure control valve. The spring 18 for setting the valve-opening differential pressure has a spring load thereof adjusted by the adjustment screw 19 screwed into an open end of the piston 34 of the second differential pressure control valve.

According to the expansion device 31 configured as above, when the automotive air conditioner is operating in the steady state, and the outlet temperature of the expansion device 31 becomes approximately 15° or less which is assumed when the automotive air conditioner serves as an air conditioner, the shape-memory alloy spring 21 senses the outlet temperature of the expansion device 31 to have the minimum spring load, and the second differential pressure control valve is closed. Now, insofar as the differential pressure ΔP between the pressure at the refrigerant inlet 12 and the pressure at the refrigerant outlet 14 is small, the first differential pressure control valve is closed, so that the expansion device 31 has a fixed restriction passage cross-sectional area determined by the cross-sectional area of the orifice 20 of the first differential pressure control valve. When the differential pressure ΔP rises to first exceed the valve-opening differential pressure set by the spring 18 of the first differential pressure control valve, the first differential pressure control valve opens, whereafter the restriction passage cross-sectional area proportionally increases as the differential pressure ΔP increases.

In the expansion device 31 as well, the shape-memory alloy spring 21 is configured such that when the automotive air conditioner is started under a high-load condition, the shape-memory alloy spring 21 senses a very high outlet temperature of the expansion device 3 to lift the valve element 33 of the second differential pressure control valve, thereby opening the valve hole 32 having a larger inner diameter than that of the valve hole 15 of the first differential pressure control valve, to allow refrigerant to flow at a large flow rate. It should be noted that when the automotive air conditioner is operating in the steady state, the second differential pressure control valve opens when the differential pressure ΔP increases until it overcomes the spring load of the spring 35, and hence the second differential pressure control valve also functions as a pressure-relief valve for avoiding abnormally high pressure in a high-pressure circuit.

In the above-described first and second embodiments, the temperature of refrigerant at the refrigerant outlet 14 is sensed by the temperature-sensing actuator formed by the shape-memory alloy spring 21, whereby it is judged that the automotive air conditioner is being started under a high-load condition. In embodiments described hereinafter, a description will be given of a case in which the pressure of refrigerant at the refrigerant outlet of an expansion device is sensed, whereby it is judged that the automotive air conditioner is being started under a high-load condition. More specifically, when the automotive air conditioner is at rest, the refrigerant inlet and the refrigerant outlet of the expansion device communicate with each other via an orifice, and hence refrigerant is equal in temperature, pressure, and density between the refrigerant inlet and the refrigerant outlet. Now, if refrigerants have the same the density, since temperature and pressure have a linear relation therebetween, it is possible to consider that sensing of the pressure of refrigerant at the outlet of the expansion device is equivalent to sensing of the temperature of refrigerant at the outlet of the expansion device. This makes it possible to cause an expansion device to have the same function as that of the expansion devices 3 and 31 according to the first and second embodiments by configuring the expansion device such that it is actuated to be fully opened when the pressure at the refrigerant outlet exceeds pressure corresponding to the refrigerant temperature of 25° in the case of the above-described example shown in FIG. 3.

FIG. 6 is a central longitudinal cross-sectional view of the arrangement of an expansion device according to a third embodiment. In FIG. 6, component elements identical to those shown in FIG. 2 are designated by identical reference numerals, and detailed description thereof is omitted.

The expansion device 41 according to the third embodiment is distinguished from the FIG. 2 expansion device 3 according to the first embodiment in that the temperature-sensing actuator of the FIG. 2 expansion device 3 is changed into a pressure-sensing actuator. More specifically, in the expansion device 41, a power element 42 that operates, when high pressure is sensed, in the direction of reducing the spring load of the spring 18 which sets the valve-opening differential pressure at which the differential pressure control valve opens, is screwed onto the hollow cylindrical portion of the body 11.

The power element 42 is formed by holding a diaphragm 45 made of a thin metal plate between an outer housing 43 having a center projected outward and an inner housing 44 having an opening in the center thereof and having a hub connected to the body 11, and welding all the outer peripheries of the housings 43 and 44 and the diaphragm 45 under atmosphere or vacuum atmosphere along the whole circumferences thereof. A hermetically sealed space formed by the outer housing 43 and the diaphragm 45 accommodates a snap plate or a disc spring 46, a spring 47, and a spring-receiving member 48. On a side of the diaphragm 45 opposite to a side thereof where the disc spring 46 is disposed, a displacement-transmitting member 49 is disposed for transmitting the displacement of the diaphragm 45 to the spring 18. A stopper 50 in the form of a step is formed on an inner wall of the inner housing 44, for restricting the motion of the displacement-transmitting member 49 in the direction of increasing the spring load of the spring 18. This inhibits the power element 42 from changing the setting of the valve-opening differential pressure at which the differential pressure control valve opens, when the automotive air conditioner is operating in the steady state.

The power element 42 has the same characteristic as the characteristic shown in FIG. 3. However, the horizontal axis represents pressure corresponding to temperature, and the vertical axis represents the stroke of the displacement-transmitting member 49 which axially moves following the displacement of the diaphragm 45.

When the automotive air conditioner is operating in the steady state and the outlet temperature of the expansion device 41 is approximately 15° or less which is assumed when the automotive air conditioner serves as an air conditioner, the pressure of refrigerant at the refrigerant outlet 14 of the expansion device 41 is low, and therefore the diaphragm 45 of the power element 42 is displaced upward, as viewed in FIG. 6. At this time, the stopper 50 restricts the motion of the displacement-transmitting member 49 to prevent the stroke thereof from being changed.

Inversely, when the automotive air conditioner is started under a high-load condition, the temperature of refrigerant at the refrigerant outlet 14 of the expansion device 41 is very high, and accordingly the pressure thereof is also high. In this case, the diaphragm 45 of the power element 42 is displaced by the high pressure toward a side where the disc spring 46 is disposed, and the displacement is transmitted to the spring 18 via the displacement-transmitting member 49, whereby the spring load of the spring 18 is reduced, and the valve-opening differential pressure at which the differential pressure control valve opens is set to zero or a very low differential pressure. With this configuration, the differential pressure control valve fully opens upon generation of even a slight differential pressure thereacross.

After the automotive air conditioner is started, the temperature of refrigerant at the refrigerant outlet 14 of the expansion device 41 progressively lowers until the power element 42 senses the pressure corresponding to temperature e.g. of 25°, whereupon the shape of the disc spring 46 is changed from a shape in which the center thereof is recessed inward into a shape in which the center thereof is inflated outward. After that, the spring load of the spring 18 is approximately linearly increased according to the reduction of the pressure. Alternately, when the power element 42 senses the pressure corresponding to the temperature of 25°, the disc spring 46 may be changed in a snap action manner such that the displacement-transmitting member 49 is brought into abutment with the stopper 50. In this case, when the power element 42 senses the pressure corresponding to the temperature of 25°, the disc spring 46 operates such that the valve-opening differential pressure at which the differential pressure control valve opens is returned to the valve-opening differential pressure at which the differential pressure control valve opens when the automotive air conditioner is operating in the steady state, and the setting of the valve-opening differential pressure is effected by adjusting the spring loads of the disc spring 46 and the spring 47. The load of the disc spring 46 is adjusted by combining a plurality of disc springs (three in the illustrated example) having respective appropriate spring loads while compensating for the deficit of the spring load with the spring 47. Further, the final fine adjustment of the spring load is performed by plastically inwardly deforming an end face of the outer housing 43 to change the position of the spring-receiving member 48 in the direction of compressing the spring 47.

It should be noted that although in the present embodiment, part of a screw thread of the body 11, which is screwed into the power element 42, is cut such that the pressure of refrigerant at the refrigerant outlet 14 easily reaches the diaphragm 45, the cut part is not necessarily required since portions of the power element 42 and the body 11 screwed together are not completely hermetically sealed.

FIG. 7 is a central longitudinal cross-sectional view of the arrangement of an expansion device according to a fourth embodiment. In FIG. 7, component elements identical to those shown in FIG. 6 are designated by identical reference numerals, and detailed description thereof is omitted.

The expansion device 51 according to the fourth embodiment is distinguished from the expansion device 31 according to the third embodiment in that the configuration of the power element 42 and the method of connecting the power element 42 and the body 11 are changed. First, in the expansion device 51, the power element 42 and the body 11 are connected by press-fitting the hollow cylindrical portion of the body 11 into the opening of the inner housing 44.

In the power element 42, the inner housing 44 thereof includes a diaphragm-receiving portion 52 which has an annular shape and has a portion opposed to the diaphragm 45 inwardly extended. The diaphragm-receiving portion 52 is useful in filling a space formed by the outer housing 43 and the diaphragm 45 with gas. The gas-filled power element 42 is formed by welding all the outer peripheries of the outer and inner housings 43 and 44 and the diaphragm 45 under high-pressure gas atmosphere to each other. After that, the power element 42 is left standing in the atmosphere until it is assembled with the body 11. In doing this, the diaphragm-receiving portion 52 receives the diaphragm 45 inflated toward an open end of the inner housing 44 by the pressure of the gas filling the inside to thereby prevent the diaphragm 45 from being deformed beyond a displaceable stroke. In the gas-filled power element 42, the spring loads of the disc spring 46 and the spring 47 accommodated therein can be reduced, and hence in the illustrated example, the number of the disc springs combined to form the disc spring 46 is reduced to two. Further, the power element 42 is configured such that a spring-receiving member 53 is interposed between the spring 47 and the disc spring 46 which are for use in adjusting the spring loads, such that the disc spring 46 is urged by the center thereof. With this arrangement, compared with the expansion device 31 according to the third embodiment, in which the spring 47 urges the disc spring 46 via a portion distant from the center thereof, it is possible to obtain a larger adjustment margin when fine adjustment of the load of the spring 47 is performed by inwardly deforming the end face of the outer housing.

FIG. 8 is a central longitudinal cross-sectional view of the arrangement of an expansion device according to a fifth embodiment. In FIG. 8, component elements identical to those shown in FIG. 6 are designated by identical reference numerals, and detailed description thereof is omitted.

The expansion device 61 according to the fifth embodiment is distinguished from the FIG. 6 expansion device 31 according to the third embodiment in that the open state of the expansion device is maintained while the automotive air conditioner is at rest in an environment with a high ambient temperature. More specifically, in the expansion device 3 according to the first embodiment, by setting the spring load of the shape-memory alloy spring 21 with which it urges when the ambient temperature is high, to a value even larger than the spring load which sets the valve-opening differential pressure to zero, whereby the valve element 16 is lifted to thereby maintain the open state of the expansion device 3 when the automotive air conditioner is at rest. In contrast, in the expansion device 31 according to the third embodiment, the pressure-sensing actuator acts only in the direction of reducing the spring load set for the expansion device 31. Therefore, even if the spring load of the spring 18 is reduced, the spring load can only be reduced to 0. This makes it impossible to maintain the open state of the expansion device 31 during stoppage of the automotive air conditioner.

To cope with the above problem, the expansion device 61 is provided with pressure-sensing follow-up means which is disposed between the displacement-transmitting member 49 and the space communicating with the refrigerant outlet 14, for axially moving back and forth according to pressure sensed by the pressure-sensing actuator. The pressure-sensing follow-up means includes a hollow cylindrical spring-receiving portion 62 axially slidably disposed in the hollow cylindrical portion of the body 11, and a spring 63 urging the hollow cylindrical spring-receiving portion 62 toward the power element 42. The hollow cylindrical spring-receiving portion 62 has an engaging portion 64 on one end thereof. When the hollow cylindrical spring-receiving portion 62 moves toward the power element 42, the engaging portion 64 is engaged with the piston 17 accommodated in the hollow cylindrical spring-receiving portion 62, for lifting the valve element 16. The other end of the hollow cylindrical spring-receiving portion 62 is formed with an adjustment screw 65 that adjusts the spring load of the spring 18 for setting the valve-opening differential pressure at which the differential pressure control valve opens.

In the expansion device 61 configured as above, when the automotive air conditioner is at rest and ambient temperature is high, no differential pressure is generated across the expansion device 61 and the power element 42 senses pressure corresponding to the ambient temperature. At this time, since the power element 42 senses high pressure, the diaphragm 45 thereof is displaced toward the side where the disc spring 46 is disposed. At this time, the hollow cylindrical spring-receiving portion 62 and the displacement-transmitting member 49 are moved toward the power element 42 by the urging force of the spring 63, in a manner following the displacement. During the process, the engaging portion 64 moves toward the power element 42 together with the piston 17, to lift the valve element 16 integrally formed with the piston 17, whereby the expansion device 61 is maintained in the open state.

FIG. 9 is a central longitudinal cross-sectional view of the arrangement of an expansion device according to a sixth embodiment. In FIG. 9, component elements identical to those shown in FIG. 7 are designated by identical reference numerals, and detailed description thereof is omitted.

The expansion device 71 according to the sixth embodiment is constructed by providing the FIG. 7 expansion device 51 according to the fourth embodiment with the pressure-sensing follow-up means. The expansion device 71 has a spring 72 disposed in the space communicating with the refrigerant outlet 14. With this arrangement, when the ambient temperature is high and the automotive air conditioner is at rest, no differential pressure is generated across the expansion device 71, and the power element 42 senses pressure corresponding to the ambient temperature, while the diaphragm 45 is displaced toward the side where the disc spring 46 is disposed. Since the spring 72 urges the piston 17, the spring 18, and the displacement-transmitting member 49 toward the power element 42, in a manner following the displacement, the valve element 16 integrally formed with the piston 17 is lifted, whereby the expansion device 71 is maintained in the open state.

FIG. 10 is a central longitudinal cross-sectional view of the arrangement of an expansion device according to a seventh embodiment. In FIG. 10, component elements identical to those shown in FIGS. 5 and 6 are designated by identical reference numerals, and detailed description thereof is omitted.

The expansion device 81 according to the seventh embodiment is distinguished from the expansion device 31 according to the second embodiment shown in FIG. 5 in that the temperature-sensing actuator is changed to the pressure-sensing actuator appearing in FIG. 6. More specifically, in the expansion device 81, the power element 42 that operates, when high pressure is sensed, in the direction of reducing the spring load of the spring 35 urging the second differential pressure control valve in the valve-closing direction is screwed onto the hollow cylindrical portion of the body 11.

When the automotive air conditioner is at rest and the ambient temperature is very high, the temperature of refrigerant at the refrigerant outlet 14 of the expansion device 81 is very high and accordingly the pressure thereof is also high. In this case, the diaphragm 45 of the power element 42 receives the high pressure to be displaced toward the side where the disc spring 46 is disposed, and the displacement is transmitted to the spring 35 via the displacement-transmitting member 49 to reduce the spring load of the spring 35 is reduced, whereby the valve-opening differential pressure at which the second differential pressure control valve opens is set to zero or a very low differential pressure. With this arrangement, the second differential pressure control valve fully opens in response to even a slight differential pressure generated thereacross, and the restriction passage cross-sectional area of the expansion device 81 is set to a passage cross-sectional area determined by the valve hole 32 having an inner diameter larger than that of the valve hole 15 of the differential pressure control valve, enabling refrigerant to flow at a large flow rate.

FIG. 11 is a central longitudinal cross-sectional view of the arrangement of an expansion device according to an eighth embodiment. In FIG. 11, component elements identical to those shown in FIG. 10 are designated by identical reference numerals, and detailed description thereof is omitted.

The expansion device 91 according to the eighth embodiment is constructed by providing the expansion device 81 according to the seventh embodiment shown in FIG. 10 with the pressure-sensing follow-up means. More specifically, in the expansion device 91, a spring 92 is disposed in the space communicating with the refrigerant outlet 14, for urging the piston 34 in the valve-opening direction.

With this arrangement, when the ambient temperature is high and the automotive air conditioner is at rest, no differential pressure is generated across the expansion device 91, and the power element 42 senses pressure corresponding to the ambient temperature to displace the diaphragm 45 toward the side where the disc spring 46 is disposed, thereby setting the valve-opening differential pressure at which the second differential pressure control valve opens, to a lower value. When pressure corresponding to the temperature of refrigerant at the refrigerant outlet 14 becomes higher than pressure setting the valve-opening differential pressure to 0, the spring 92 urges the piston 34, the spring 35, and the displacement-transmitting member 49 toward the power element 42, in a manner following the displacement of the diaphragm 45. This causes the valve element 33 integrally formed with the piston 34 to be lifted, whereby the expansion device 91 is maintained in the open state.

The preferred embodiments of the present invention have been described heretofore, but the present invention is by no means limited to the preferred embodiments. Although in the above-described embodiments, the actuator for setting the valve-opening differential pressure at which the second differential pressure control valve opens to a lower value is configured such that it directly senses the temperature or pressure of refrigerant at the refrigerant outlet, this is not limitative, but the actuator may be configured such that it senses the temperature or pressure of refrigerant in a low-pressure circuit connected to the refrigerant outlet. This is because in the low-pressure circuit extending from the refrigerant outlet of the expansion device to the refrigerant inlet of the compressor, the temperature and pressure of refrigerant are substantially the same at the start of the automotive air conditioner. For example, as shown in FIG. 1, when the expansion device 3 is mounted in the heat exchanger 6, the actuator may be configured such that it senses the temperature or pressure of refrigerant at a low-pressure inlet of the heat exchanger 6, or when the expansion device 3 is mounted in the evaporator 4, the actuator may be configured such that it senses the temperature or pressure of refrigerant at a refrigerant outlet of the evaporator 4.

In the expansion device according to the present invention, when the refrigeration cycle is exposed to a high-temperature state before the start of the automotive air conditioner, the differential pressure control valve is in an open state or in the state capable of opening in response to a very low differential pressure. Therefore, it is possible to allow refrigerant to flow at a large flow rate immediately after the start of the automotive air conditioner. This makes it possible to eliminate the inconvenience that when the automotive air conditioner is started under a high-load condition, the flow rate of refrigerant circulating through the refrigeration cycle becomes short to make it difficult to cool the automotive air conditioner.

The foregoing is considered as illustrative only of the principles of the present invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and applications shown and described, and accordingly, all suitable modifications and equivalents may be regarded as falling within the scope of the invention in the appended claims and their equivalents. 

1. An expansion device for expanding refrigerant circulating through a refrigeration cycle, comprising: a differential pressure control valve that is responsive to differential pressure between pressure at a refrigerant inlet and pressure at a refrigerant outlet, to open; and an actuator that sets valve-opening differential pressure at which said differential pressure control valve opens, to a lower value, when refrigerant at the refrigerant outlet is higher in temperature than a temperature at which the refrigeration cycle is operating in a steady state or higher in pressure than pressure corresponding to the temperature.
 2. The expansion device according to claim 1, wherein said actuator is a shape-memory alloy spring which senses a temperature of the refrigerant at the refrigerant outlet, and is operable when the temperature of the refrigerant becomes higher than the temperature at which the refrigeration cycle is operating in the steady state, to increases a rate of increase in load thereof to thereby set the valve-opening differential pressure at which said differential pressure control valve opens, to a lower value, or thereby open said differential pressure control valve.
 3. The expansion device according to claim 1, wherein said actuator senses pressure of the refrigerant at the refrigerant outlet to thereby convert the pressure to a stroke in a direction of opening or closing said differential pressure control valve, and is operable when the sensed pressure becomes equal to pressure corresponding to a temperature higher than the temperature at which the refrigeration cycle is operating in the steady state, to increase the stroke to thereby set the valve-opening differential pressure at which said differential pressure control valve opens to zero or a very low differential pressure.
 4. The expansion device according to claim 3, wherein said actuator includes a stopper for inhibiting the valve-opening differential pressure from being changed for said differential pressure control valve, when said actuator senses the pressure of the refrigerant at the refrigerant outlet corresponding to the temperature at which the refrigeration cycle is operating in the steady state.
 5. The expansion device according to claim 3, wherein said actuator is a power element that hermetically holds a diaphragm between a first housing having a center projected outward and a second housing having an opening in a center thereof, and has a snap plate or a disc spring provided within said first housing, for supporting said diaphragm as said diaphragm is displaced inward by receiving the pressure of the refrigerant at the refrigerant outlet, and for being largely displaced inward when the pressure becomes equal to the pressure corresponding to the temperature higher than the temperature at which the refrigeration cycle is operating in the steady state.
 6. The expansion device according to claim 5, wherein said second housing of said power element includes a diaphragm-receiving portion which has an annular shape and has a portion opposed to said diaphragm radially inwardly extended, and wherein a space formed by said first housing and said diaphragm is filled with gas.
 7. The expansion device according to claim 5, comprising pressure-sensing follow-up means for axially moving said differential pressure control valve back and forth by following displacement of said diaphragm, and wherein said differential pressure control valve is maintained in an open state when said diaphragm senses pressure even higher than pressure which sets the valve-opening differential pressure to
 0. 8. An expansion device for expanding refrigerant circulating through a refrigeration cycle, comprising: a first differential pressure control valve that is responsive to differential pressure between pressure at a refrigerant inlet and pressure at a refrigerant outlet, to open; a second differential pressure control valve that has a valve hole formed between the refrigerant inlet and the refrigerant outlet, and has a diameter larger than that of said first differential pressure control valve; and an actuator that sets valve-opening differential pressure at which said second differential pressure control valve opens, to a lower value, when refrigerant at the refrigerant outlet is higher in temperature than a temperature at which the refrigeration cycle is operating in a steady state or higher in pressure than pressure corresponding to the temperature.
 9. The expansion device according to claim 8, wherein said actuator is a shape-memory alloy spring which senses a temperature of the refrigerant at the refrigerant outlet, and is operable when the temperature of the refrigerant becomes higher than the temperature at which the refrigeration cycle is operating in the steady state, to increases a rate of increase in load thereof to thereby set the valve-opening differential pressure at which said second differential pressure control valve opens, to a lower value, or thereby open said second differential pressure control valve.
 10. The expansion device according to claim 8, wherein said actuator senses pressure of the refrigerant at the refrigerant outlet to thereby convert the pressure to a stroke in a direction of opening or closing said second differential pressure control valve, and is operable when the sensed pressure becomes equal to pressure corresponding to a temperature higher than the temperature at which the refrigeration cycle is operating in the steady state, to increase the stroke to thereby set the valve-opening differential pressure at which said second differential pressure control valve opens to zero or a very low differential pressure.
 11. The expansion device according to claim 10, comprising pressure-sensing follow-up means for axially moving said second differential pressure control valve back and forth by following a change in the stroke, and wherein said second differential pressure control valve is maintained in an open state when the sensed pressure becomes even higher than pressure which sets the valve-opening differential pressure at which said second differential pressure control valve opens to
 0. 